If you're skeptic, try it out some time lol. Anyone that has seriously used one, and didn't really know how to use it, will say that the rest of the night wasn't too pleasant.

Yes, it does take more then one person to do.
Yes, sometimes its nothing bad and nothing happens. But most times, something does happen, one way or another, big or small.

If you did try it and only asked yes/no or any other simple questions like "What's your name? How old are you?" so on so forth, that's just lame. If you said "Hey make the lights flicker on and off if you're real" sometimes, if not most times, it does happen.

Lol I guess this goes for anyone else xD. I'm not crazy-ish for nothing you know.

Alright so it's 3:50 AM, and I'm in bed looking at that video. I saw the part where there was the head popping out of the window above the dresser, and the replay zoomed in and it was a face and that sent shivers down my spine.
Then I saw the part where the girl is down the hall on the floor, the guy shuts the door, changes his mind and looks again, and she is there standing. Oh man... that was frickin weird.
(If you have no idea what the hell I'm talking about, go here: http://br.youtube.com/watch?v=CW-oQ7HAB5U&NR=1)

But I must say that the part you mention with the moving furniture and all that looks very unrealistic. The camera was positioned in a way where you could see most of everything that moved, but it would have been easy for some guy and a buddy to just throw that stuff around while still remaining unseen to the camera.

The base thing that happens with these sorts of phenomenon is simple attribution theory. Example: I bet almost every one of us knows someone who INSISTS that they can make streetlamps blow out. Why? Because it happens to them. Walking along, and BAM! Streetlight pops out. I will admit it happens to me too. That must mean the light is popping in response to our presence, right? Of course it doesn't.

It doesn't mean anything. The only reason people remember lights going out is because, well, they remember lights going out. How many times do you walk down the street and the lights stay on? How many people run home and write: "Dear Diary, nothing of strange or unusual consequence happened today." I assure you that if you DID write that, along with the weird stuff, you would see that the non-weird dwarfs the weird soundly.

So, where does the weird come from? Well, it comes from your imagination. It comes from strange (but natural) things...several of those "ghosts" looked like mini dust devils (have you ever seen those type of mini-tornados? They are common where I grew up (western Iowa), any place with lots of wind and lots of dust and/or fog. They do look eerie, but they are not supernatural. And some things are just flat-out hoaxes.

Nothing in that video or any video I have ever seen has spooked me in the slightest. Ghosts aren't real.